Radio Noise from PV System

Comments

Sounds like, in this case, there is a lot of differential noise coming through too (ferrites not working, buried shielded twisted cable between CC and solar array--noise from solar array).

If that is the case, differential filtering with ferrites is going to be hard with 60+ amps of DC current.

The DC power filter that I listed in my earlier post should be about as good as one will get with differential and common mode external filtering for DC with off-the-shelf components. Anything else would probably need a redesign of the internal circuitry.

The nice thing about the DC Power Filter is that it is rated for use on input power lines (upwards of 2kV --- if I recall correctly). Should be pretty rugged and safe.

that filter might work ok bill. i see a resistor across the 2 leads and do wonder of its value as this will be a constant bleed off of power and most likely is not critical for the filter to work. hams are cheap at times and many would not pay much for such a filter. i think he could succeed in getting rid of enough of it on his own and he could wind the coils as possibly bifilar. maybe some suggestions as to how dimensions and number of turns he might try, but i didn't relook as to the current he needs to know what gauge he may need. aw heck, maybe just wind them with insulation on and you won't need to worry of shorts and this may be trial and error to a point.

Quite a few good suggestions already. Here is what I would try,
same direction windings of the + and - PV wires around an iron pipe and put decoupling caps across +/- wires at both ends .

The same direction windings (both clockwise or counter-clockwise since the return DC current is in the opositedirection already) would cancel out the DC magnetics to keep the iron pipe from saturation. More the turns, more likelyhood to balance out the DC magnetics. With the iron pipe not magnetically saturated, the windings now would act like a high impedance inductor due to the high permeability of iron. But this is a poor transformer to cancel out the 24Khz component and harmonics (but this "high-Z Pi filter" might attenuate quite a bit already). If this gives good attenuation but not enough, try making more and cascade them.

Try the same on a toroidal ferrite. This is a good transformer to cancel out the 24KHz components but a slight imbalance in the DC magnetics might saturate the toroid to keep it from functioning as a transformer for the 24KHz noise.

Vic, type 43 has permeability around 800 and 31 around 1500. So, you would need near twice the turns on type 43 to achieve the same effect on type 31.

Ed,
This may make you laugh.... I use to install marine single side bands with pactor for e-mail and it was the same kind of thing for Hams thru the free service. We had this very nice $1,000 dollar analyzer that would tell you where the problem was occurring. One day it fell off the mast near a radar into a very nasty marina in 15 feet of water. The rest of the year I used an AM radio tuned off station to locate and test noise sources. It worked very well!

I did the same with a dual array system with an XWCC and the MX60. From 3 feet the MX60 was very loud where the XWCC took about a foot to be noticeable. Totally unscientific but usefull! I'd go spend $500 and shipping, it is a much better unit. But if you are married to Outback do all the stuff that others have suggested!

First, in using ferrites, one needs to find a large core, ideally a Toroid, large enough in diameter, and with large enough window area that one can pass a number of turns of wire through the toroid. In my situation, common-mode filters work well enough that no other filter has been required. Have used a STACK of four Type 31 Toroids (taped together), and passed four turns of a PAIR of #6 GA wire through the cores (a bifilar winding). One of these was placed on the PV in conductors to the MX-60 CC, right at the MX. This was effective, HOWEVER, My PV runs are all in pipe, the MX to Battery runs are in pipe, ALL AC conductors are in pipe and so on. In addition, the power room is a large metal box -- a sea cargo container. I built my power system assuming that the MPPT CC and Invertrers would create a lotta noise, and tried to contain it from the start. The primary reason for my off-grid location was to move away from all of the switching power device noise and power line noise present in ever-increasing amounts in towns and cities.

My power system still generates its own noise, but the noise power on lower frequencies is about 5000 times lower than at my in-town location. This is a large improvement. I have been unscientific in my approaches to noise reduction, as had started with the assumption that all of the power system would generate noise, and would need to be contained and attenuated from the beginning, and antennas would need to be separated from the power system as much as possible. Others have not had that luxury.

So in summary, for ferrite chokes to be most effective, they need to be large, to accommodate multiple turns of wire through them. In my opinion, one is trying to develop enough Effective Series Resistance to offer high attenuation at frequencies of interest. In my situation, Common-Mode filters using stacked Type 31 material have been adequate, but have not tried eliminating this filter to see the difference without it.

I have not tried a Low Pass Filter in the PV leads, but think that this may be a good experiment for Ed, as getting ferrites for the job are probably days away srom SD, but he probably has the parts at hand for the LPF, and so on.

My off-grid location is without internet, and am on the way there in a few hours, so will be off-line for some time. Good Luck, Ed, and this board has a number of bright, interested and knowledgable folks present. And, boB has designed a number of MPPT CCs, and is a Ham, so I would defer to him on this sutff. 73 GL Vic K6IC

The ferrites aren't going to do anything because dI/dt is phat and anything that can be put around the PV conductors isn't going to be able to store enough energy in the magnetic field (see "saturated") to help.

That depends on the source of the noise. If it is from internal timing circuits, while dI/dt might be relatively high, the signal level itself should be pretty low and easily swamped out by ferrites. If the noise is coming from actually switching high amperage (which I suspect is the case with the FM), then it will probably need something bigger, such as a large ferrite toroid

Iron cores - such as used in transformers, or just some hunk of iron - will be almost totally useless at higher frequencies.

I agree with WindSun, am sure that the bulk so to speak fo the NOISE is coming from the items doing the most work -- the power FETs which are banging a large inductor with many amps of I. These switching wavdeforms have very fast edges -- rich in harmonics. Fast edges result in lower losses than slow edges.

If you can find a 2.40-inch core, I'd stack some of them, tape them together, wind a # of bifilar turns through them, and try these as a Common-Mode choke on PV input.

However, Ed may have some luck building a LPF with items he has on-hand, as an initial experiment. As noted previsusly, might start with 20-30 turns #10 (or larger, depending on breaker rating etc) wire on pvc form. Use caps on input and output etc, as noted previously ... Just an experiment ...

Whatta I know ? The type 31 material is effective at Ed's freq of interest -- about twice that of type 43.When winding a few turns on a core, this difference multiplies IMHO. Some of the Ferrites and Iron cores are insanely EXPENSIVE. Have spent $25.00+ ea for some 2.40-inch cores in the past. IIRC, a recent bulk purchase of 2.40-inch Type 31 cores yielded about $5.00 ea at 1,000 units. .

OK GL Ed. RFI suppression can be similar to Grounding issues. Some think of these things as VooDo magic. But several RFI reduction approaches often add, and can result in a meaningful improvement. YMMV, so on. All The Best, Vic

i'm kind of anxious to hear from ed on any results he is getting. as to the bifilar coil, he can wind a small amount of excess lead-in from the pvs (both + and - leads wound together and not meant as a short circuit) evenly around a small piece of pvc pipe and secure it from moving. the more turns the better. if he has no excess or very little of it then he would need new wire to wire in the coils.

I spent 7 hours today on trying to cure the 24 khz harmonics. The capacitance seems to do the most good and seemed most effective at 160M and 80M.

Here is my benchmark with things hooked up as normal
early today.

At 13.9994 mhz it is S-5
At 10.097 it is S 5 ½
At 6.988 it is S 9+3 db
At 3.614 it is S-9+3 db
At 1.832 it is S-9+7 db

Here are the readings late in the day hooked up as normal.
At 13.9994 mhz is S-5
At 10.097 is S-5 1/2
At 6.988 is S-9+3 db
At 3.614 is S-9 +3 db
At 1.832 S-9 +7 db

They seemed to read the same early this morning and a little bit ago so the benchmark test seem very valid.

Results of tests:

.1 and .022 capacitors to ground and across the PV Input

At 13.9994 mhz it is S-5 ½ (worse)
At 10.097 it is S-6 ½ (worse)
At 6.988 it is S-9+3 (same)
At 3.614 it is S 7 ½ (Improvement)
At 1.832 it is S 8 ½ (Improvement)

Result of test:
.1 and .022 capacitor to ground and across the PV input
Added .02 in metal can used for EMI to ground on the PV inputs

At 13.994.0 mhz it is S-3 ½ (reduced 1.5 S units)
At 10.097 it is S-5 ½ (reduced 1.0 S units)
At 6.988 it is S-8 ½ (reduced about 1.0 S unit)
At 3.614 it is S-5 (reduced about 2.5 S units)
At 1.932 it is S-6 ½ (reduced abpit 2 S units)

I tried with both leads running through the ferrite and with the ferrite on separate leads and none of this helped at all. I had as many as
14 cores on each wire. It tried 31 turns of #10 wire about 2" in diameter close spaced and tired it around a steel pipe and PVC pipe and I seen no improvement. It varied the spacing and tried less turns all to no avail.

I tried a Carcom EMI filter with no improvement.

Result of PV Input TEST:
In place of the PV input to the FM80 I used 48 VDC of batteries and used 3 foot of twisted wire between the battery and the FM80. It definitely reduces the level of interference so putting the PV input wire in conduit would very likely help even though there may be some panel radiation. I would of thought I could of dropped it to zero at least at the higher frequencies but such was not the case. It was very low at 13.9994 mhz but it was audible. This test may be a little "bogus" but the reading on the FM80 looked OK. It should be more valid than shutting off the panels as the FM80 keeps working. I did the same on the FM80 output(used a battery and 3 foot of twisted wire) and seen no improvement so I don't think it is a very significant source of the interference. I also removed the remote temperature sensor and it made absolutely no difference. It looks like the PV input is the radiator.

It looks like with putting the PV Input in conduit and using capacitors to ground and across the PV Input one could get the level very low at 14 mhz and up. I would estimate S1 on my benchmark test. It appears one can get a decent improvement below 14 mhz but it is still very loud.

COURSE OF ACTION: I am going to think about it for a few days as I have run out of ideas! Right now I am inclined to try a Xantrex MPPT or wait for the Morningstar MPPT. I could also get a non-MPPT controller as I have not read any reports of them having interference problems. At least the interference level should be reduced with any of these 3 options and if it still needs improvement I can try the things I did today.

Thanks so much to everyone for some great inputs. It was very kind of you to put all the effort in thinking and writing the e-mails. I will keep everyone posted. BTW for the remote repeater sites we are going to luck out as the harmonics fall such that our inputs(where we receive) fall about half way between each harmonic so we won't have interference at the sites even with the FM80. I confirmed this today with another set of tests.

Those caps will be fine for the higher harmonics, but to kill the fundamental, which will kill the harmonics, you need lots of Tantalum Lo-ESR caps. They might be $10 ea, you need as many uF at the PVmax +20% as you can stuff in a steel box. 500uF, 800uF @ 90V or whatever . The Lo-ESR caps are designed for switching power supplies, and 24KHz should be in their useful freq range.

Digikey, Mouser , Newark have them, many are surface mount, but you can always solder some braid to them.

If you are around 24V, might even look at some of the car stereo "super caps" 3F should do it!

you have time to tinker before a new cc comes and i'm sure you're not in a hurry to buy the xw tomorrow so try adding even more capacitance. got any .47uf caps you can try leaving the ones you already have in place? even paralleling more .1uf caps to the ones already in place to get a higher overall uf value would due. see if it drags down your interference even further as caps are cheap. heck, you can even throw an electrolytic across the pv + and -. just be sure it can handle the oc voltage the pvs might throw at it and observe polarity.
hmm. thinking. (some smoke) maybe try a tantalum electrolytic capacitor as they handle high frequencies better than standard electrolytics.

That depends on the source of the noise. If it is from internal timing circuits, while dI/dt might be relatively high, the signal level itself should be pretty low and easily swamped out by ferrites. If the noise is coming from actually switching high amperage (which I suspect is the case with the FM), then it will probably need something bigger, such as a large ferrite toroid

Iron cores - such as used in transformers, or just some hunk of iron - will be almost totally useless at higher frequencies.

When I was studying covert channel sniffing, during my InfoSec / Crypto / Spook days, we studied how changes in power can radiate all over the place.

In the case of switching supplies, they ripple their input all the way back to the source, which is really great if someone wants to spy on you.

I am interested in the Low-ESR capacitors since capacitors has been the only thing that has given any improvement. Since it is cold where the
controller I will have to have them rated for -20F. I need to get some conduit supplies and a metal box so I have some room and can have
real short leads on the capacitors.

I think I have some #31 material I could try but I am not optomisic as I have not seen any measure able improvement where with the
capacitors I can definitely get quite a few db of improvement.

i was going by what he may have on hand as many will have e caps with 25-50v ratings on hand. higher voltage e caps are less common due to price, low capacitance, and size, but i say whatever he can get working for him is good. in fact it may be good to place a cap or 2 up at the pvs if possible.

That depends on the source of the noise. If it is from internal timing circuits, while dI/dt might be relatively high, the signal level itself should be pretty low and easily swamped out by ferrites. If the noise is coming from actually switching high amperage (which I suspect is the case with the FM), then it will probably need something bigger, such as a large ferrite toroid

This is generally true, but with the presence of a strong magnetic field (by the large PV's DC current), the ferrite is magnetically saturated i.e. dB/dt~0 (edited to correct from dH/dt, B is saturated on the magnetic B-H curve), the ferrite would provide no inductive effect.

It tried 31 turns of #10 wire about 2" in diameter close spaced and tired it around a steel pipe and PVC pipe and I seen no improvement. It varied the spacing and tried less turns all to no avail....I tried a Carcom EMI filter with no improvement

These tell me the birdies on the +/- PV wires is of differential-mode nature, not common-mode as we thought. The "bifilar" windings or the Cor.com EMI filter is for common-mode noise with the presence of strong DC feed currents. The bifilar winding helps neutralizing the strong "DC" magnetic field to be able to use ferrites but this winding has no inductive effect for differential-mode noise.

.... In place of the PV input to the FM80 I used 48 VDC of batteries and used 3 foot of twisted wire between the battery and the FM80. It definitely reduces the level of interference

This gives some hope. The twisted wire would provide "very mild" inductance in each of the + / - wire paths separately and be able to do some filtering (or it could be the shorter length would not radiate as much ?).

My suggestions:
* Don't use any ferrites since these would be rendered ineffective by the strong "DC" magnetic field.
* Use "xx turns of #10 wire about 2" in diameter close spaced and tired it around a PVC pipe" separately on the + and - wires. Put them in steel boxes or "aluminum wrapped" and ground them. The LF birdies could use these "coils" as antenna to radiate.
* Do use de-coupling caps across + / - wires on both ends of these "coils". The caps toward the PV end would provide a low impedance return path for the noise instead of up and radiating via the PVs.
* If this arrangement works, it could be improved by "reverse windings" of the + / - wires on the same PVC pipe. Your earlier trial with bifilar windings proves there is good "cross transform" between the wires, but unfortunately to nullify the inductive effect for this differential-mode birdies. The "counter windings" i.e. one clockwise, one counter-clockwise and crossed each half turn, for symetry, would provide stronger inductive effect for differential mode signals (than separate windings on each path).
* You might want to throw in the Cor.com EMI filter in series (closer to the FM) just to see if there is any additional benefit in case there is some common-mode noise since the "counter windings" has no effect on common-mode noise.

This is generally true, but with the presence of a strong magnetic field (by the large PV's DC current), the ferrite is magnetically saturated i.e. dB/dt~0 (edited to correct from dH/dt, B is saturated on the magnetic B-H curve), the ferrite would provide no inductive effect.

One thing I cannot find out much info on is how much saturation you get if you run both wires through the ferrites. Ferrites seem to work fairly well on AC flourescent lights, typically 40 or 80 watts when they are placed across both wires - but that is AC in a twisted pair.

I'm new here, but may have some experience to really take a bite out of this problem.

I work with PWM switching 30-120A at 48VDC and 80 MHz RF power at 1 kW+, and making it comply to FCC (usually Class A) limits.

N.B Without detailed design info on the controller, I can only make an educated guess.

Here I outline the problem and its nature:

However, any controller of this type will be switch mode (with or without inductors) or else have a LARGE heatsink to dissipate a lot of power (which is a very counterproductive waste of power from expensive PV arrays)

With the switchmode fact established (and proven by your RFI data), I can address this.

Most likely most of yuor noise is differential mode coming from the controller onto the wires, as others have said.

At LF (<=2 MHz, 1.8 MHz as you cite) your antennas are in the near field, which requires more aggressive suppression than would otherwise be needed. Fortunately, it is relatively straightforward to aggressively filter differential noise here

At higher frequencies, 2 MHz to ~200 MHz, less filtering is required due to the ~1/f power spectrum emission from PWM waveforms. In this range, filters can be fairly effective if built carefully.

At 200-600 MHz, suppression is difficult due to parallel stray C and series stray L on even surface mount components. Fortunately,you indicate no real problems here.

Now to fixes:

1. Get rid of the LF differential mode noise.

Build a filter on a PCB, back side is ground plane, return to the - controller terminal. No ground plane under the inductors.

Use a 1 uH ferrite inductor on the + input terminal of the controller in series with the array. A 2x2 series-parallel combination of Vishay/Dale IHLP5050FDER1R0M01 (Digi-Key 541-1032-2-ND) at www.digikey.com will carry 60A safely. Now add a Panasonic EEU-EE2C221 (Digi-Key P/N P13626-ND) 220 uf/160V electrolytic cap from the PV array side of the inductor to the - input terminal on the controller.

Parallel this cap with a 0.1 uf/250V SMT 1206 X7R ceramic cap (short and fat PCB copper areas-not traces- with a back side ground plane on the PCB. The PCB areas going to the - terminal need to be very short and very fat. Also parallel 1000 pf and 10 pf NP0 SMT caps at 200V+ as well.

The ferrite inductor won't saturate until ~80-100A, and will absorb some VHF energy. The electrolytic works against the L to pull the LF stuff down by ~30 dB and is rated at 100 kHz, has low Z in the 10s of MHz. The 0.1 uf goes up to ~30 MHz, the 1000 pf to ~80 MHz and the 10 pf to several hundred MHz. Stray L on these caps will reduce their effectiveness.

If this isn't enough:

2. Try this in the - lead instead (but reverse the electrolytic cap!)

If still not enough:

3. Try in both + and - leads, but return the grounds to the case.

If still not enough:

4. Get rid of the common mode noise:

An appropriate common mode choke/filter on the PV array side of the L network I just described should minimize further noise. Return its ground to the controller case, and bond those to earth ground (if allowable.)

If still not enough:

Leave the input fixes in and

Try Steps 1-4 on the output too.

Also, if it works but the filtering is insufficient, multiple L networks can be cascaded to increase the attenuation. The cutoff F is ~12 kHz for the lowest pole.

For the "standard" common mode choke--the pair should go through as a "bundled pair"... The differential flow of power current (one +, on -) cancel each other out--so the DC field from a DC pair running through the choke should be zero.

For common mode current--for example imagine all of the wires tied together at the source and a signal generator driving all the wires "up and down" at the same time with respect to earth ground--is a common mode signal. For the above wrap around the common mode choke/inductor/filter--these common mode current is what generates a net non-zero magnetic field--which appears as a reactive (inductance) counter force to the common mode noise--an (almost) equal and oposite counter voltage to block the common mode current flowing through the choke. Put a capacitor to shield/chassis ground near/at the source side to further "short circuit" the current flow directly back to the source and further prevent energy from broadcasting out the length of wire.

The issue here may be that much/most of the noise is differential mode... So, you need to add inductance directly in the DC current flow to block high frequency noise (low pass filter). Anything that increases this inductance needs to support the entire DC current -- hence leading to saturation problems (where the magnetic material does not become more magnitized--The saturated low pass filter element now behaves like an inductor at lower frequencies / high current changes and nearly like a wire at high frequencies--or useless at blocking high frequency interference.

The success in the florescent fixture with a common mode filter is that this is blocking the common mode emissions and really not doing anything for differential mode noise (the old fixtures use magnetic ballasts--so they probably do a pretty good job of blocking differential noise). The common mode noise issue is probably the result of the arc lamp coupling with the metal (earth grounded) reflector--something that a common mode filter is good at blocking.

BTW, if you are skeptical of the low Z an electrolytic cap can have in the 10s of MHz, you may be justified in many instances, but exceptions do exist as shown below:

This is from measurements I've done on Panasonic EE and FC series caps.

1. they are inductive at >~100 kHz, ~10-20 nH.

2. I measured one at 30-80 MHz on a network analyzer (and was quite surprised at how low its Z really was at that frequency range.) Note that this was a Panasonic FC series part, rated for switchmode power supply service.

3. Caps can still be effective bypasses above resonance if the L is a low enough value at the frequency of interest.

Welcome aboard. Yea--we posted "at the same time" so I did not see your response before submitting mine.

In the end--trying to patch on filters on a less than ideal switch mode design can be frustrating and may ultimately be impossible to make it work for your needs (short of installing the whole thing in a sealed metal box with the patched on low pass filters).'

Be careful with the inductors given (nice surface mount devices)--they may need active cooling at 60 amps (approximately 40C rise).

Noise from a switcher is almost always introduced by some parasitic capacitance, such as the FET-to-heatsink interface in a DC-DC buck. This is also coincidentally the one point in the circuit (the switching node) that experiences the greatest dV/dT, and so is capable of an incredible amount of both radiated and conducted EMI if it isn’t contained properly. There are several things you can do if they aren’t already part of the design (and if you’re comfortable tinkering with the inner workings of your controller). Putting a small (0.1 – 1uF) ceramic capacitor across the DC rail (+ to -) RIGHT AT the drain of the upper FET(s) can help. Add another similar capacitor between the aforementioned drain and the actual heatsink. And finally, if the chassis ground and the circuit ground aren’t tied together, add one more capacitor between the circuit ground (as close to the source of the lower FET(s) – or the anode of the freewheeling diode – as you can get) and the actual heatsink. Make sure all capacitors are rated for the max input voltage (200v would be a wise idea), and keep the leads as short as possible. The idea is to form a path for the noise that returns it to its source as quickly as possible, and make the path as small as possible. Otherwise it’s going to find its way into all sorts of unpredictable places, seeking a way to get back to the controller, and black magic is what you’ll need to sort that out.

Also, a few comments about what has already been said here. Ferrites will generally not saturate with a differential current if you’re using them as a common-mode choke (passing both wires through with equal turns and tight coupling). Differential currents tend to produce a net zero magnetic flux within the core. Common-mode currents (which will be only small amplitude noise) will be presented with a high impedance. But since common-mode noise typically behaves as a current source, you need to provide a low-impedance path at your frequency of interest so the noise can return to the source (decoupling caps). Otherwise you may end up making the noise problem worse, since a current source will attempt to increase its voltage in order to overcome any impedance.

My guess is, since you have only two wires, the noise is differential in nature. Common-mode noise requires a separate return path, which is typically “ground.” To suppress differential noise once it escapes from the controller, you might have to resort to a powdered iron core that will pass the required DC current without saturating. This will probably mean a fairly large core for your application.

The inductors I gave will only need active cooling if the ambient where they are running is over 40 degrees C. They could be heatsunk or fan cooled if required, but a larger area PCB with lots of copper will also help. Also a 3x3 array (9 inductors(!) in series-parallel) would run significantly cooler.

About patching on filters: In EMI, it is often better to specify or design quieter stuff from the beginning and do less filtering/shielding.
Do get the quieter controller--and be prepared to filter it too if its "as-built" noise emissions are still too much IN YOUR APPLICATION. I didn't focus on that soo much as others already have done so.

I agree that patching on filters can be risky. EMI is always an unpredictable tiger to tame because of so many unknown variables some call "black maginc."

But even a quiet controller may not be "quiet enough" with a sensitive amateur receiver and good antenna in the near field, making additional measures necessary.

I use these type of filters in industrial equipment to tame the conducted noise from 30-120A PWM switching with good success. But I also design for low RF emissions as well in the first place.

In place of the PV input to the FM80 I used 48 VDC of batteries and used 3 foot of twisted wire between the battery and the FM80. It definitely reduces the level of interference

Ed W0SD

This is VERY interesting and gives me an idea... At least something to try...

Do this again, except this time, when monitoring the noise level on your receiver, re-connect just ONE (1) PV wire to the array. I bet the signal goes up again, but my question is, does it go up by the same amount it did before with the PV fully connected ??? If it was only differential mode noise, then then the noise level will not go up by that much when you reconnect those PV wires. At the same time, add the ferrite around that one PV wire you just connected (a few turns) and of course you will be assured it will not have any hope of saturating during that test as well.

Also, you ~may~ have to move your receiver frequency to an adjacent 25 KHz birdie because of the design of the FM80 controller. You may notice that, depending on the actual FM80 PWM % at any given time, that alternate birdies are at different receive levels. This is what I found years ago when working with the MX60 and and HF receiver with dipole located above our PV array.